The present disclosure relates to improvements in apparatus for grinding the hard metal inserts or working tips of rock drill bits (percussive or rotary), tunnel boring machine cutters (TEM) and raised bore machine cutters (RBM) and more specifically, but not exclusively, for grinding the cutting teeth or buttons of a rock drill bit or cutter.
In drilling operations the cutting teeth (buttons) on the drill bits or cutters become flattened (worn) after continued use. Regular maintenance of the drill bit or cutter by regrinding (sharpening) the buttons to restore them to substantially their original profile enhances the bit/cutter life, speeds up drilling and reduces drilling costs. Regrinding should be undertaken when the wear of the buttons is optimally one third to a maximum of one-half the button diameter.
Manufacturers have developed a range of different manual and semi-automatic grinding machines including hand held grinders, single arm and double arm self centering grinding machines and grinders designed specifically for mounting on drill rigs, service vehicles or set up in the shop.
These types of machines utilize a grinding machine having a spindle or rotor rotated at high speed. A grinding cup or grinding pin, mounted on the end of the rotor or spindle, grinds the button and typically the face of the bit/cutter surrounding the base of the button to restore the button to substantially its original profile for effective drilling. In addition to the rotation of the grinding cup, these types of grinding machines may include features where the grinding machine is mounted at an angle to the longitudinal axis of the button and the grinding machine is rotated to provide orbital motion with the center of rotation lying in the center of the grinding cup. When grinding the buttons, the centering aspects of the grinding machine tend to center the grinding machine over the highest point on the button.
The conventional grinding machines switch between grinding pressure and balance pressure to achieve the desired effect. In conventional grinding machines, the minimum grinding pressure is equivalent to the weight of the arm or lever section and the components attached to it.
Longstanding problems with these types of grinding machines are vibration and noise due to high rotational speeds, wear, the requirement for large compressors for pneumatic systems and long grinding times per button, in the larger sizes.
U.S. Pat. No. 7,402,093 addressed a number of problems with earlier machines and provided a grinding machine carried on a support system where the grinding cup is rotated at variable speeds preferably from about 2200 to 6000 RPM and the support system is capable of providing a variable feed pressure preferably or optionally up to 350 kilos. In this type of machine there is a need to control the feed pressure with precision.